TAJO-1338: Defines RESTful API for Clients

[ykrips]

Detail API designs can be found in the following link.
https://cwiki.apache.org/confluence/display/TAJO/TAJO+REST+API

[ykrips]

This patch aligned to current version of source code.

[ykrips]

Testcases in travis-ci failed, but testcases in apache build servers has been passed. Please see details in the following link.
https://builds.apache.org/job/PreCommit-TAJO-Build/695//testReport/

[blrunner]

Currently, it looks like unused variable.

[blrunner]

+1

Great! It looks good overall to me and I found that rest server response successfully on my laptop as follows.

$ curl -XGET 'http://localhost:26880/rest/databases'
{"databases":["default","information_schema"]}

$ curl -XGET 'http://localhost:26880/rest/databases/default/tables'
[{"tableName":"customer","external":true},{"tableName":"lineitem","external":true},{"tableName":"nation","external":true},{"tableName":"orders","external":true},{"tableName":"part","external":true},{"tableName":"partsupp","external":true},{"tableName":"supplier","external":true}]

$  curl -XGET 'http://localhost:26880/rest/cluster'
{"workers":[{"connectionInfo":{"id":-2105400716,"host":"192.168.219.106","peerRpcPort":28091,"pullServerPort":64176,"queryMasterPort":28093,"clientPort":28092,"httpInfoPort":28080},"diskSlots":0.0,"cpuCoreSlots":1,"memoryMB":1024,"usedDiskSlots":0.0,"usedMemoryMB":0,"usedCpuCoreSlots":0,"maxHeap":932184064,"freeHeap":365067488,"totalHeap":458227712,"numRunningTasks":0,"numQueryMasterTasks":0,"lastHeartbeatTime":1428221077181}]}

I leaved some trivial comments and I found unused methods in WorkerConnectionInfoResponse and WorkerResponse, too. Before you ship this, please check my comments. :)

[ykrips]

@blrunner ,
I have removed unused methods in my patch. Thanks for review.

[blrunner]

Thanks @ykrips

I found the updated patch. Finally, could you trigger this for CI build or upload the patch to JIRA?

[ykrips]

No problems. I don't have any privileges on travis ci, so I will upload the patch to JIRA.

[blrunner]

I found the result of jenkins build as following:
https://builds.apache.org/job/PreCommit-TAJO-Build/709//testReport/

Ship it. :)

[ykrips]

@blrunner ,
Thanks you for quick review. This patch will commit into main branch.